The field of electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) has recently achieved successes linked with the development of aberration correctors, enabling atomically-resolved spectroscopy. Also, a new generation of monochromators is emerging, providing improvements in energy resolution and unprecedented access to low energy-loss ranges (optical and near IR spectral ranges). Similarly, recent progress in the collection of visible-range photons emitted by a sample has enabled novel cathodo-luminescence (CL) experiments in STEM. In addition, new ways of exploiting fast electron beams, including combining them with photon beams, have opened up the field of nano-optics, providing a high-spatial resolution alternative to conventional optical techniques.
Examples will be given on the use of spatially-resolved core-level excitation signals for quantitative measurement of electron densities [1] 2D electron gases or charge transfert at interfaces [2] in oxide-based nanodevices or for probing chemical functions in graphene oxyde. Developments in EELS and CL for reaching plasmon signatures down to the IR spectral range will be described, allowing the mapping of eigen modes in plasmonic nanostructures and a deep understanding of the physics of these excitation [3]. New possibilities for exploring the link between a crystal structure (h-BN), its defects and its emission properties as revealed by nano-CL and original quantum nano-optics experiments will be discussed [4].
[1] M. Marinova et al, Nano Lett., 2015, 15 (4), 2533
[2] M. Gibert et al, Nano Lett., 2015, 15 (11), 7355
[3] A Tararan et al, Chem. Mat. 2016, 28, 3741
[3] A. Losquin, et al, Nano Lett., 2015, 15 (2), 1229 [4] R. Bourrellier et al, Nanolett., 2016, 16 (7), 4317
Photonic & plasmonic nanomaterials , Optical properties of nanostructures
